PCT Patent Application Publication WO 02/075754 describes a resistor assembly comprising a trim resistor element enclosed within a two-piece housing. The trim resistor element includes an electrically resistive film disposed on a substrate and is received in a recess in a polymeric housing body. A housing top is bonded to the housing body to enclose the trim resistor and has an opening exposing the resistive film. Wires extend through the housing for electrical connection with the film. Following assembly, a laser beam is directed through the opening to remove a portion of the resistive film to adjust the resistance to a desired value. Following trimming, the opening is preferably sealed with a polymeric material. The product assembly is suited for use as a component in an automotive electrical system and may be inserted within a sheath of a wiring harness.
The two-piece housing requires two molding operations, with associated tooling, and a bonding operation that significantly contribute to the cost of the assembly. Also, care is needed in assembling and covering the trim resistor element within the recess to avoid damage to the electrical connection. Further, the lateral dimensions of the housing need to be sized to allow a suitable bond to be formed between the polymeric body and top without damage to the trim resistor element, which may add to the overall size of the trim resistor element and complicate insertion into the wiring harness. Still further, clearance between the trim resistor element and the housing may allow the trim resistor element to vibrate within recess during use and may lead to damage to the electrical connections.
Thus, there is a need for a trim resistor assembly that encapsulates the trim resistor element within a polymeric housing without a bonding operation and eliminates clearances about the trim resistor element within the recess of the housing, while nevertheless allows access to the resistive film for purposes of trimming the resistance.